The present invention relates to a vehicle seat, particularly to a vehicle seat designed to reduce an impact which is applied to a neck of an occupant when a vehicle is collided from behind.
Conventionally, at the time of a so-called rear collision, such as when an automobile is collided from behind, or when the automobile is collided while rolling backward, there is a risk that the head of a seated occupant is abruptly tilted backward due to inertial motion, thereby causing the neck of the occupant to receive an impact.
For this reason, in order to protect the head or the neck of the occupant against the impact exerted by the rear collision and reduce the impact applied to the neck, a seat in a vehicle such as an automobile is equipped at an upper part of a seat back with a headrest for receiving the head of the occupant from behind. Although the headrest is able to significantly reduce the impact which is applied to the neck when the vehicle is collided from behind, it is still desired to further reduce the impact applied to the neck.
In view of overcoming such a problem, there has been suggested a seat back designed to reduce the impact applied to the neck, in which an occupant is moved rearward at the time of a rear collision, so that a headrest can be moved forward by a moving load, to support the head of the occupant (refer to Japanese Patent Application Publication No. 2003-341402 (“the '402 Publication”), for example).
On the other hand, there has been known a technique that, in a vehicle seat providing a seat back in which a cushion material is disposed on a front side of a seat back frame, a portion of a seat back where a chest region of an occupant comes into contact with the seat back when a rear-end collision occurs is defined to have a smaller spring modulus and to have a greater damping coefficient than those of the other portion of the seat back (refer to Japanese Patent Application Publication No. 2005-028956 (“the '956 Publication”), for example).
In the technique disclosed in the above '402 Publication, backward movement of the chest region of the occupant is received by a pressure receiving member, while the headrest is caused to move forward in conjunction with the backward movement of the pressure receiving member. This requires a separately installed mechanism for moving the headrest, which is disadvantageous in that costs are increased and that it prevents reduction of thickness of the seat back.
In the technique disclosed in the '956 Publication, the portion of the seat back contacted by the chest region is composed of a cushion material having both a lower modulus of elasticity and a lower repulsive elasticity than those of a cushion material for the other portion in order to suppress a rebound of the chest region and decrease a relative speed between the head and the chest region in view of softening the impact applied to the neck. However, because the seat cushion is composed of a combination of multiple types of cushion materials which differ in repulsive elasticity, the technique has a disadvantage of cost increase. Further, there is another disadvantage in that it is difficult to reduce the thickness of the seat back because the cushion material of low repulsive elasticity having a certain extent of thickness should be used to sufficiently suppress the rebound of the chest region.
In view of the above-described problems, various embodiments of the present invention are directed to provide a vehicle seat capable of efficiently reducing an impact which is applied to the neck of an occupant at the time of a rear collision while maintaining a structure suitable for reducing cost and thickness.
According to an embodiment, the problems set forth above are solved by a vehicle seat comprising a seat back and a headrest attached to the seat back, in which the seat back comprises a seat back frame providing a pair of side frame sections composed of pipe shaped members at least in part, spaced apart from each other in a lateral direction, and extended in a vertical direction, and providing an upper frame for coupling upper sides of the pair of side frame sections, and the seat back further comprises a cushion material disposed at least on a front side of the seat back frame. Further, in the vehicle seat, each of the pair of the side frame sections provides a flat section obtained by deforming a region of one of the pipe shaped members opposed to the other pipe shaped member to reduce a thickness of the side frame section, a core cavity section formed by removing a portion of the cushion material opposed to the side frame section is formed in a region of the cushion material located on a front side of the side frame section, and a thickness of a region of the cushion material in which the core cavity section is formed is smaller than a thickness of another region of the cushion material for supporting a back of an occupant who is seated on the vehicle seat.
According to the above-described structure, because the flat section is formed by deforming in the region of the side frame section where the pipe shaped members are opposed to each other in order to reduce the thickness of the side frame section, areas protruded from the right and left side frame sections to a direction along which the side frame sections are opposed to each other can be removed, to broaden a distance between the pair of side frame sections in an area where the occupant has a greater lateral width without changing external dimensions of the seat back frame in the lateral direction. In this manner, interference from the right and left side frame sections that hinders the occupant from moving rearward when the occupant sinks into the seat back is suppressed, which allows the occupant to more smoothly sink into the seat back from the backrest front surface. Accordingly, quick approach of the head of the occupant to the headrest at the time of the rear collision is realized, and the impact applied to the neck is effectively reduced.
In addition, because sinking motion of the occupant at the time of the rear collision can be ensured only by shaping the side frame section, without necessity to install a separate mechanism such as a headrest shifting mechanism and without involving an increase in the number of parts, both cost and thickness can be reduced in the vehicle seat capable of softening the impact which will be applied to the neck when the vehicle is collided from behind.
It is preferable that the cushion material has a core cavity section obtained by partially removing the cushion material in a region of the cushion material located on the front side of the side frame section and opposed to the side frame section.
As such, by forming the core cavity section, a thickness of the cushion material is reduced in a region where the cushion material is deformed through physical contact with the flat section while the occupant is sinking into the vehicle seat, to facilitate deformation of the cushion material without deteriorating a proper seated feeling during normal use. It is therefore possible to effectively reduce resistance to deformation of the cushion material. In this way, smoother sinking of the occupant into the seat back from the backrest front surface is realized without involving an increase in the number of parts. Moreover, the formation of the core cavity section can contribute to further reduction of the thickness. Therefore, while maintaining low cost and thin profile, the head of the occupant can be immediately moved closer to the headrest at the time of the rear collision, to achieve more effective reduction of the impact applied to the neck.
In the above-described structure, the flat section is preferably formed at least in a place corresponding to a chest region or a shoulder region of the occupant who is seated on the vehicle seat. With this configuration, the distance between the pair of the side frame sections can be increased in an area corresponding to a part of the occupant having a greater lateral body width, without changing external dimensions of the seat back frame in the lateral direction.
Further, in an embodiment, the core cavity section is preferably formed at least in an area opposed to the region where the flat section of the side frame section is formed.
In this way, when the core cavity section is formed in the area of the cushion material opposed to the region where the flat section of the side frame section is formed, the cushion material can be formed thinly in the region of the cushion material deformed through physical contact with the flat section of the side frame section, to facilitate deformation of the cushion material. Accordingly, the resistance to deformation of the cushion material can be reduced in an effective manner. This allows the occupant to more smoothly sink into the seat back from the backrest front surface. Thus, the head of the occupant can immediately be moved closer to the headrest at the time of the rear collision, to effectively reduce the impact applied to the neck.
Moreover, in an embodiment, the flat sections are preferably angled toward mutually opposite directions relative to a back and front direction of the vehicle seat in such a manner that a distance between front ends of the opposing flat sections becomes greater than a distance between back ends of the opposing flat sections.
According to the above configuration, with the flat section formed along the shape of the back of the occupant, a distance between the back of the occupant and the side frame section can relatively be extended without greatly changing the structure of the seat back frame. In addition, because variations of the distance between the back of the occupant and the side frame section that vary by location can be suppressed, the cushion material is relatively uniformly deformed rearward during sinking motion. So, a partial increase of the resistance to deformation can be prevented. As a result, the interference from the side frame sections that hinders the occupant from moving rearward is further relieved to allow the occupant to more smoothly sink into the seat back from the backrest front surface. Thus, the head of the occupant can immediately be moved closer to the headrest at the time of the rear collision, and the impact applied to the neck can accordingly be reduced in an effective manner at low cost.
According to embodiments of the vehicle seat described above, the impact applied to the neck is effectively reduced because smoother sinking of the occupant into the seat back from the backrest front surface when the vehicle is collided from behind is realized and thereby the gap between the head of the occupant and the headrest is quickly minimized. In addition, it is also possible to effectively reduce the impact applied to the neck of the occupant at the time of the rear collision while maintaining the structure suitable for reducing the cost and the thickness.
Further in addition to allowing the occupant to more smoothly sink into the seat back from the backrest front surface, low cost and further reduction in thickness can be achieved without deteriorating a proper seated feeling during normal use.
Moreover, according to embodiments of the vehicle seat described above, resistance to deformation of the cushion material can be made relatively uniform during sinking motion, which allows the occupant to more smoothly sink into the seat back from the backrest front surface without greatly changing a configuration of the seat back frame.